Boost Control: Boost Control Solenoid Operation
Boost Control Solenoid Operation
- Before we move on, there are a couple of aspects of the solenoid's operation that are worth discussing in a little detail.
The first is the operating frequency or how many cycles per second the solenoid will happily work at.
If you drive the solenoid at a frequency that's too slow, the boost will tend to oscillate up and down slightly at the frequency of the solenoid.
And this may be accompanied by an audible pulsing of the boost pressure.
This obviously isn't desirable and a higher frequency can help eliminate this.
If you raise the frequency too high, though, the solenoid won't have enough time to operate properly and it won't work at all.
- Somewhere in between is a happy median and most boost solenoids will operate well with a frequency of 15 to 20 hertz.
Along with the frequency, there's also a dead band at the high end and low end of the operating duty cycle where the valve essentially won't function.
I'll explain this a little more thoroughly.
For a popular valve, such as the MAC solenoid, for example, if you provide it with a duty cycle of five percent, the valve won't operate.
It's as if the duty cycle is still zero and the valve remains closed.
It's not until you get past about 12 to 15 percent duty cycle, that the valve will start operating normally.
Likewise, at the high end of the duty cycle, you'll find that anything higher than about 85 to 90 percent, will end up having the valve fully open.
So, for the mech valve, the useful range where we actually have control over the boost pressure is approximately 12 to 88 percent.
It's important to understand this as it will influence the values we can use in our boost control tuning once we start setting up the system.